The functional and structural importance of hydrophobic associations within the electron transport system of the mitochondrial inner membrane will be characterized by studying two of its major electron transport complexes, cytochrome bc1 and cytochrome c oxidase. The individual protein-lipid complexes, their multi-subunit fragments and individual subunits will be investigated with respect to: 1) molecular size, shape and possible asymmetry; 2) possible domain structure; 3) functional importance, specificity and affinity of the membrane combining sites for phospholipids; 4) identification of subunits in direct contact with the hydrocarbon interior of the phospholipid bilayer; and 5) amino acid sequence of polypeptide chains in direct contact with the apolar environment of the membrane. Phospholipid and detergent exchange, detergent binding, hydrophobic chemical labeling, and hydrodynamic physical measurements will be used to investigate these structural and functional features of the complexes. The long range goal of this project is to identify the hydrophobic interactions that are esential for coupled electron transport within the mitochondrial inner membrane and to characterize the functional importance of the protein-lipid interface between intrinsic membrane protein complexes and the apolar interior of membranes.